Loam
Start at the trailhead, not the weather app
Forecasts are useful. So are rainfall totals and a trail condition estimate. But when you arrive, the trail gets a vote.
Look at the first section of tread. Is it firm under your shoe? Does it hold its shape when you step on it? Are there wet spots that look shallow but feel soft underneath? You do not need to turn a trailhead check into a science experiment. You just need to notice what the ground is doing.
The rule worth remembering
Wet is not automatically bad. Soft is the problem. If the tread deforms under you, give it more time.
Look for the places that dry last
A trail can feel firm for most of a climb and still have a few sections that are not ready. Those sections are often more useful than the sunny, dry parts when you are making the call.
Low spots
Water collects wherever the trail gives it a place to sit. A puddle is obvious. A dark patch with a soft edge can be harder to spot.
Flat turns
Water moves downhill. Flat corners and benches can hold moisture longer than the sloped trail leading into them.
Shaded tread
Sections under dense trees may get less sun and wind. They can stay soft after an exposed section has dried.
Clay and fine soil
Fine soil can feel firm on top while remaining soft below. A shoe or tire that sinks through the surface is a warning.
Your tires will tell you too
Pay attention to what sticks to the tires during the first few minutes. A little damp dirt is normal. Thick mud building up on the tread is different.
Watch for a tire leaving a clean, deep groove behind it. If you can see the tread pattern stamped into soft dirt, the trail is not ready for normal traffic. Do not keep riding just because the next section looks better. The damage happens in the soft section.
Do not let one good section fool you
Drying is rarely uniform. A trail can cross open ground, enter trees, climb a slope, and dip into a drainage area within a few minutes. Each piece gets a different amount of sun, wind, and water.
That is also why a regional "two days after rain" rule is so unreliable. Conditions can change within the same network, and they can change again during the day as the surface warms or another shower moves through.
When in doubt, ride somewhere else
There is no prize for being the first rider back on soft tread. If the official status is unclear, check it. If the condition looks marginal, take the extra time to look at the trailhead. If the ground is clearly deforming, leave.
The best wet-weather ride is the one that does not leave evidence that you were there.
The science behind the estimate
Loam starts with a simple physical fact: a trail does not dry just because the rain stops. Water has to enter the ground, move through or across the soil, and leave the trail environment. How quickly that happens depends on the soil, terrain, vegetation, recent weather, and how wet the ground already was.
Soil controls infiltration
Soils do not accept water at the same rate. USDA hydrologic soil groups range from high-infiltration soils such as deep sands and gravels to very slow-infiltration soils associated with clay, high water tables, or restrictive layers. Typical infiltration-rate ranges used in the hydrologic-group framework run from more than 0.30 in/hr for Group A to less than 0.05 in/hr for Group D when thoroughly wet.
Previous rain still matters
A storm does not start with an empty soil profile. USGS notes that soil already saturated from previous rainfall cannot absorb much more, so a larger share of the next storm becomes runoff. Recent weather therefore matters even when the latest storm was not especially large.
Terrain changes the water path
Slope changes how quickly water can move away from a surface. Low spots, drainage features, and trail geometry can change where water collects or leaves the tread. Soil classification and slope are separate pieces of the landscape, which is why both matter to a trail-condition model.
Drying is a water budget
After rainfall, water can remain in the soil, move downward or sideways, run off, or return to the atmosphere through evaporation and plant transpiration. Soil-water-balance models use these processes to estimate changing soil moisture and net infiltration over time.
Why Loam is not a rain timer
There is no useful rule that says every trail becomes rideable after the same number of dry hours. Starting moisture, infiltration behavior, terrain, canopy, and weather after the storm all change the answer.
That is the problem Loam is designed to estimate. The model combines public soil and terrain information with recent weather and network characteristics to estimate how conditions are changing. It is a model of likely trail conditions, not a sensor embedded in the dirt, and it never overrides an official closure.
What the research says
USDA and USGS hydrology work treats infiltration, soil moisture, runoff, canopy, land cover, slope, and evapotranspiration as interacting parts of the water cycle. Recent trail research adds an important piece: rainfall intensity and accumulated rainfall can strongly affect runoff and sediment generation on recreational trails, while wet conditions make trail surfaces more vulnerable to degradation.
USDA NRCS: Hydrologic Soil Groups
Soils are classified by infiltration and runoff behavior when thoroughly wet. The framework distinguishes four main groups and dual drained/undrained classes.
NRCS National Engineering Handbook →USGS: Infiltration and the Water Cycle
Explains how soil characteristics, saturation, land cover, slope, and evapotranspiration affect where precipitation goes.
USGS Water Science School →USGS: Soil-Water-Balance
A published water-budget model that estimates soil moisture, net infiltration, evapotranspiration, and canopy interception from gridded environmental data.
USGS SWB Version 2.0 →NRCS: RUSLE2
A USDA model for estimating soil loss caused by rainfall and associated overland flow, connecting rainfall and runoff to erosion risk.
USDA NRCS RUSLE2 →Fang & Ng, Journal of Environmental Management, 2026
A year-long field study found cumulative rainfall and maximum daily rainfall predicted runoff and sediment yield on recreational trails, with maximum daily rainfall the stronger predictor in that study.
Read the research →These sources describe the physical processes and research Loam draws from. They do not describe Loam's proprietary model or disclose its weights and thresholds.